Field of the Invention
This invention relates to high temperature, lightweight ceramic insulation such as porous carbon tile comprising carbon, silicon and oxygen. More particularly, the invention relates to a lightweight, ceramic carbon insulation comprising carbon, silicon, and oxygen which is capable of retaining its shape and strength when exposed to an oxidizing environment at temperatures as high as 1700.degree. C. and to the method of preparation which comprises combining carbon substrates with a reaction product derived from the reaction of di- and trifunctional silanes to form a gel and, subsequently heating or pyrolyzing the gel and the carbon substrate, in an inert atmosphere, to form the high temperature, lightweight ceramic insulation.
Space vehicles such as the space shuttle, which leave and reenter the earth's atmosphere, require exterior thermal insulation. The operation of the space shuttle requires the development of lightweight and thermally efficient exterior insulation capable of withstanding a variety of environments. During reentry into the earth's atmosphere, the insulation must maintain the vehicle's exterior structure below 175.degree. C. while experiencing substantial aeroconvective thermal environments which heat the surface of the insulation to temperatures in excess of 1,000.degree. C. In space, the thermal protection must insulate the vehicle from the cold (e.g., -70.degree. C.) experienced while in orbit. In addition to thermal and aeroconvective environments, the insulation must be able to withstand the mechanical stress associated with launch vibrations, acoustics, structural movement of the vehicle's surface, and landing impacts.
For example, lightweight ceramic state-of-the art thermal insulation tiles, as developed by Lockheed (LI-900) and NASA/Ames Research Center (AETB, AIM, FRCI, etc.), are limited to use-temperatures of about 1300.degree. C. in an oxidizing environment. For applications which experience temperatures above 1300.degree. C., a dense ceramic material must be used which adds a substantial weight penalty. Presently, thermal insulation used for protecting space vehicles includes both rigid and flexible ceramic insulation with a carbon composite being used on the leading edges of the vehicle. However, these ceramic carbon composites must be very porous in order to maintain their weight at a reasonably low level. This could be accomplished by using the ultra-high temperature, lightweight, ceramic carbon insulation of this invention.